CN109960137B

CN109960137B - Method for manufacturing balance wheel of clock

Info

Publication number: CN109960137B
Application number: CN201811455309.4A
Authority: CN
Inventors: A·埃梅利; F·盖斯萨斯; J-C·马丁; L·帕拉特; Y·温克勒; G·迪多梅尼科; P·温克勒; J-L·黑尔费尔; L·通贝兹; B·伊诺; D·W·科森; M·维勒明
Original assignee: Swatch Group Research and Development SA
Current assignee: Swatch Group Research and Development SA
Priority date: 2017-12-22
Filing date: 2018-11-30
Publication date: 2021-04-09
Anticipated expiration: 2038-11-30
Also published as: CN112965355A; US11307535B2; CN109960137A; JP6770049B2; EP3502787B1; JP2019113533A; US20220163923A1; EP3502787A1; US11640140B2; EP3796102A1; EP3796102B1; US20190196408A1

Abstract

The invention relates to a method for manufacturing a metal alloy balance wheel by moulding, comprising the following steps: a) a mould made in the negative shape of the balance (1); b) obtaining a metal alloy having a coefficient of thermal expansion of less than 25ppm/° c and capable of being in an at least partially amorphous state when heated to a temperature between its glass transition temperature and its crystallization temperature; c) placing said metal alloy in said mould, heating said metal alloy to a temperature between its glass transition temperature and its crystallization temperature, so as to be thermally moulded and form a balance; d) cooling said metal alloy to obtain a balance (1) made of said metal alloy; e) releasing the balance (1) obtained in step d) from its mould.

Description

Method for manufacturing balance wheel of clock

Technical Field

The invention concerns a method for making a balance for a timepiece, the balance comprising a felloe, a hub and at least one arm connecting the hub to the felloe.

Background

The oscillator or resonator of a mechanical timepiece consists of a spiral spring and a flywheel called a balance. Temperature changes change the stiffness of the spiral spring and the geometry of the balance spring and balance wheel, which changes the spring constant and inertia, and thus the oscillation frequency. Clock manufacturers strive to obtain temperature stable oscillators, and have explored/utilized several approaches, one of which obtains the Nobel prize, developed for the Charles-Edouard Guillame Elinvar alloy, which has an elastic modulus that increases with temperature and compensates for the increase in balance inertia. The development of oxidized, and therefore thermally compensated, silicon has since exceeded the performance of the alligator alloy and has the advantage of being less sensitive to magnetic fields. The spiral spring made of monocrystalline quartz also allows thermal compensation of the inertial variations of the balance. But in contrast to oxidized silicon, which has an oxidation thickness that can vary depending on the material of the balance used, quartz spiral springs are limited to materials with a coefficient of thermal expansion of about 10 ppm/deg.c, for example corresponding to titanium and platinum. The main problems with these materials are processability and control of fine structure and/or finishing processes (e.g. mirror polishing). In the case of titanium, its relatively low density limits its use for large balances, and in the case of platinum, its high price limits its use to prestige and luxury goods.

Disclosure of Invention

The aim of the present invention is to remedy these drawbacks by proposing a method for making a balance wheel using new materials, allowing simpler and more precise manufacturing, for example to reduce the variations in momentum and/or variability in the same production batch.

To this end, the invention firstly relates to a method for manufacturing a balance for a timepiece, the balance comprising a rim, a hub and at least one arm connecting the hub to the aforementioned rim, the rim, hub and arm being made of a metal alloy, the method comprising the following steps:

a) a mould made in the negative shape of the balance wheel (negative shape);

b) obtaining a metal alloy having a coefficient of thermal expansion of less than 25ppm/° c and capable of being in an at least partially amorphous state when heated to a temperature between its glass transition temperature and its crystallization temperature;

c) placing a metal alloy in a mould, heating said metal alloy to a temperature between its glass transition temperature and its crystallization temperature, so as to be thermally moulded and form a balance;

d) cooling said metal alloy to obtain a balance made of said metal alloy;

e) releasing the balance obtained in step d) from its mould.

The invention also relates to a method for manufacturing a balance for a timepiece, the balance comprising a rim, a hub and at least one arm connecting the hub to the aforementioned rim, the hub and the arm being made of a metal alloy, the rim being made of a material having a density higher than the density of the aforementioned metal alloy of which the hub and the arm are made, said method comprising the following steps:

a) a mold made in the negative shape of the balance;

a') inserting a rim or rim portions made of a material having a density higher than that of the above-mentioned metal alloy into the mould;

b) obtaining a metal alloy having a coefficient of thermal expansion of less than 25ppm/° c and capable of existing in an at least partially amorphous state when heated to a temperature between its glass transition temperature and its crystallization temperature;

c) placing a metal alloy in a mould, heating said metal alloy to a temperature between its glass transition temperature and its crystallization temperature so as to be hot-moulded, and overmoulding said felloe or felloe portion so as to mould a balance with an insert;

d) cooling the metal alloy to obtain a balance wheel with an insert;

e) releasing the balance obtained in step d) from its mould.

Due to the nature of amorphous metals, metal alloy balances can be produced using simplified manufacturing methods (e.g., casting methods or hot molding methods). Furthermore, one characteristic of a metal alloy in its at least partially amorphous form is that it has a significantly wider range of elastic deformation than its crystalline equivalent, due to the absence of dislocations. This characteristic makes it possible to perform overmoulding or integration so that it is possible to improve the centring and to control the inertia and/or unbalance elements in the balance.

Drawings

Other features and advantages will become apparent from the ensuing description, given for indicative and non-limiting purposes only, with reference to the accompanying drawings, in which:

fig. 1 is a perspective view of a balance made according to the invention;

fig. 2 is a partial top view of an alternative balance made according to the invention;

fig. 3 is a partial top view of another alternative balance made according to the invention;

FIG. 4 is a section along the axis A-A in FIG. 3; and

figures 5 to 10 are partial top views of other balance wheel alternatives made according to the invention.

Detailed Description

Fig. 1 shows a balance 1 for a timepiece. Such balance 1 conventionally comprises a continuous or discontinuous felloe 2 defining the outer diameter of balance 1 and a hub 4 constituting a central part thereof and containing a hole 6 defining the pivot point of balance 1, which receives a shaft (not shown). The hubs 4 are commonly connected to the rim 2 by arms 8. In this example, there are four arms 8 at 90 ° to each other. There are also balances with two or three arms, arranged at 180 ° or 120 °, respectively.

According to the first embodiment, the rim 2, the hub 4 and the arms 8 are made of the same metal alloy. Balance 1 is advantageously a one-piece component, i.e. it is manufactured in one piece.

Balance 1 may, for example, be made entirely of an alloy containing platinum or palladium, as described in detail below. Since platinum has a particularly high density (21,000 kg/m)³) Therefore, the platinum alloy used in the present invention also hasHas high density (15.5 g/m)³) It is therefore not necessary to add components made of elements with a high density to increase the inertia of the balance.

To this end, according to a first embodiment of the invention, the method of manufacturing balance 1 in which rim 2, hub 4 and arm 8 are made of the same metal alloy comprises the following steps:

a) a mould made in the negative shape of balance 1, said mould comprising a possible decorative surface structure;

b) obtaining a metal alloy having a coefficient of thermal expansion typically below 25ppm/° c and capable of being in an at least partially amorphous state when heated to a temperature between its glass transition temperature and its crystallization temperature;

d) cooling said metal alloy to obtain a balance 1 made of said metal alloy;

e) releasing balance 1 obtained in step d) from its mould.

The cooling step d) may be carried out at a cooling rate selected to obtain a crystalline, partially amorphous or fully amorphous alloy.

For example, balance 1 may also be made entirely of an alloy containing titanium or zirconium, as will be described in detail below. Since zirconium, for example, has a relatively low density, the zirconium alloy used in the present invention also has a relatively low density (6.5 g/m)³) It is therefore proposed to add components made of a more dense material to increase the inertia of the balance, in particular if it is desired to have a small size for a small movement. These components make it possible to increase the inertia of the balance while maintaining an aesthetic rim geometry and good aerodynamic characteristics.

Thus, according to a first alternative shown in fig. 2, the rim 2 can comprise an overmoulded first inertia adjusting member 10, the first inertia adjusting member 10 being made of a material having a density higher than that of the metal alloy. These first inertia adjusting members 10 may be made of tungsten or tungsten carbide, for example, and obtained by over-molding.

To achieve this object, the method of the present invention comprises: a step of overmoulding the above-mentioned first inertia adjustment member 10 into the rim 2 by means of an insert placed in the mould before the metal alloy is introduced and overmoulded, said first inertia adjustment member 10 being made of a first material having a density higher than that of the above-mentioned metal alloy.

According to a second embodiment, the arms and the hub of the balance are made of a metal alloy and the rim is made of a material having a density higher than the density of the metal alloy used for the arms and the hub. The material itself may be a metal alloy containing platinum or palladium or other material as defined below. The arm and the hub of the balance are made, for example, of an amorphous metal alloy containing zirconium, as defined below, so as to allow the balance to be paired with a spiral balance spring, preferably made of monocrystalline quartz, and, in order to improve the inertia of the balance, the rim is made of another material having a density greater than that of the zirconium-containing metal alloy used for the arm and the hub.

In order to achieve this, according to a second embodiment of the invention, the hub 4 and the arms 8 of a balance for a timepiece are made of a metal alloy, the rim 2 being made of a second material having a density higher than that of the metal alloy from which the hub 4 and the arms 8 are made, the method for manufacturing such a balance comprising the following steps:

a) a mould made in the negative shape of balance 1;

a') inserting a rim or rim portions made of a material having a density higher than that of the above-mentioned metal alloy into a mould;

c) placing a metal alloy in a mould, heating said metal alloy to a temperature between its glass transition temperature and its crystallization temperature so as to be hot-moulded, and overmoulding the felloe or said felloe portion so as to mould a balance with an insert;

d) cooling the metal alloy to obtain a balance wheel with an insert;

e) releasing the balance obtained in step d) from its mould.

The method according to the invention according to the first or second embodiment advantageously exploits the characteristics of a metal alloy which, when heated, can be at least partially in amorphous form, in order to produce a balance made of a metal alloy.

Indeed, metal alloys that are capable of being in an at least partially amorphous form when heated allow for greater ease of molding by allowing parts having complex shapes to be produced with greater precision. This is because of the special property of "amorphous metals" which can be softened while remaining amorphous for a certain period of time in a particular temperature interval [ Tg-Tx ] specific to each alloy (for example, for Zr-containing alloys: Tg 440 ℃, Tx 520 ℃). They can therefore be shaped at relatively low stress and not too high a temperature, allowing simplified processes, such as thermoforming, to be used. Furthermore, the use of such a material makes it possible to reproduce the fine geometry rapidly and precisely according to the temperature within the temperature interval [ Tg-Tx ], the alloy therefore having all the details of the negative shape. For example, for a platinum-containing material as defined below, the molding is carried out at about 300 ℃ with a viscosity of up to 103Pa · s and a viscosity of 1012Pa · s at a pressure of 1MPa, instead of at the temperature Tg. The use of a die has the advantage of producing three-dimensional parts with high precision, which cannot be achieved by cutting or punching.

The method advantageously used is the formation of amorphous preforms. The preform is obtained by melting in a furnace the metallic components constituting the metallic alloy. The melting is carried out under a controlled atmosphere in order to obtain as low as possible an oxygen contamination level of the alloy. Once these components are melted, they are cast into the shape of a semi-finished product and then rapidly cooled to partially or completely maintain the amorphous state. Once the preforming is completed, thermoforming is carried out, with the aim of obtaining the final part. The hot molding is performed by pressing for a period of time in a temperature range between the glass transition temperature Tg and the crystallization temperature Tx of the metal alloy such that an at least partially amorphous structure is maintained. This is done to maintain the elastic properties of the amorphous metal.

In the case of Zr containing alloys and temperatures of 440 c, the pressing time generally need not exceed about 120 seconds. Thus, the thermal molding makes it possible to maintain the initial amorphous state of the preform. The various forming steps of the cast solid balance according to the invention are then:

1) the mould with the negative shape of the balance is heated to a selected temperature,

2) the amorphous metal preform is placed between hot dies,

3) applying a clamping force to the mold to impart the geometry of the mold to the amorphous metal preform,

4) waiting for the maximum time of the pre-selection,

5) the mould is opened and the mould is opened,

6) a cooling balance wheel, and

7) the balance is removed from the mould.

The balance wheel may of course also be produced by casting or injection. The method comprises casting or injecting a heated metal alloy at a temperature between its glass transition temperature and its crystallization temperature such that it can be at least partially amorphous in a mold having the shape of the final part.

The mold may be reused or dissolved to release the part. The moulding method has the advantage of perfectly reproducing the balance geometry, which includes possible decorations or surface structures. A smaller degree of inertia and centering variation is obtained in the production batch of balances. The moulding method makes it possible to obtain a balance with an aesthetic geometry, sharp internal angles, rim profile and/or convex arm profile and perfect final surface. A discontinuous rim may also be provided. To achieve the highest quality, the mold will be made of silicon by the DRIE [ deep reactive ion etching ] method. It is self-understood that the mold may also be constructed by mechanical milling, laser machining, electro-erosion, or any other type of machining.

The elastic properties characteristic of amorphous metal are used for overmoulding or integrating functional and/or decorative elements in the rim and/or at the position of the arms and/or at the position of the hub, for example by placing a suitable insert in the mould before the heated metal alloy is made at least partially amorphous between its glass transition temperature and its crystallization temperature.

Independently of the first or second embodiment of the method of the invention, the rim 2 can comprise a groove 12, the groove 12 being designed to receive a

second member

14, 15 for adjusting the inertia and/or the unbalance, as shown in figure 3. These grooves 12 can advantageously be provided during the manufacture of balance 1 by moulding according to the method of the invention. The second means 14, 15 for adjusting inertia and/or unbalance may be, for example, a counterweight, a split counterweight acting as a counterweight, a pin 14, a cotter pin or an unbalance adjustment pin 15. These components are pressed or clamped into the respective recesses 12. Fig. 3 shows the pin 14 inserted into its groove 12, and the unbalance adjustment pin 15 inserted into its groove 12. Fig. 4 shows a cross section along the line a-a of fig. 3. Fig. 3 shows the unbalance adjustment pin 15 inserted in the groove 12 of the rim 2.

It is evident that these means for increasing the inertia of the balance are preferably used in the case where the felloe is made of a material with a low density, such as titanium or zirconium, but they can also be used in the case where the felloe is made of another material.

To increase the inertia of the balance, it is also possible to provide a thicker or wider rim, in particular in the case of a larger balance.

The recess 12 shown in fig. 3 may also be a recess designed to receive an aesthetic and/or light emitting element, such as a tritium tube (not shown) or a capsule of phosphorescent (e.g. high-intensity noctilucent) or fluorescent material.

According to another aspect of the invention, one or another step of the method comprises the step of overmoulding the

flexible centring members

16, 17 onto the periphery or surface of the hub 4. Thus, the hub 4 may comprise an integrated flexible centring member which allows the balance to self-centre on the axis during its assembly, due to the elastic deformation of the above-mentioned flexible centring member.

According to fig. 5, the above-mentioned integrated flexible centering members 16 are shown as elastic strips within the inner circumference of the hub 4, such that the integrated flexible centering members 16 are located in the holes 6. According to fig. 6, the above-mentioned integrated flexible centering members 17 are located on the surface of the hub 4 and distributed around the hole 6. According to the method of the invention,

flexible centring members

16 and 17 can advantageously be inserted by moulding during the manufacture of balance 1.

According to another aspect of the invention, one or other of these methods comprises a step of overmoulding a third flexible

inertia adjustment member

19, 20, 22a, 22b in the arm 8. At least one of the arms 8 thus carries an integrated third flexible inertial adjustment member.

According to fig. 7, the end of the arm 8 on the side of the rim 2 ends in two

branches

8a, 8b, between which

branches

8a, 8b a space 18 is formed, in which space 18a third "V" -shaped flexible bistable inertial adjustment element 19 is integrated for the purpose of adjusting the frequency.

According to fig. 8, the space 18 accommodates a third flexible inertial adjustment member 20 for the purpose of adjusting the frequency. To this end, the third inertia adjustment member 20 is made of a material such as silicon or silicon oxide having different expansion characteristics than the metal alloy of the balance of the invention.

According to fig. 9, the end of the arm 8 on the side of the rim 2 ends in three

branches

8a, 8b, 8c, between which three

branches

8a, 8b, 8c two

spaces

18a, 18b are formed, in which two

spaces

18a, 18b a third flexible multistable inertia-adjusting

ratchet member

22a, 22b is integrated for the purpose of adjusting the frequency.

According to the method of the invention, these third flexible

inertial adjustment members

19, 20, 22a, 22b for adjusting the frequency can also advantageously be put in place by moulding during the manufacture of balance 1.

These third flexible

inertia adjustment members

19, 20, 22a, 22b for adjusting the frequency can be used when the whole balance is made of the same metal alloy and when the arms are made of one metal alloy and the rest of the balance, in particular the rim, is made of another material. .

According to another alternative of the invention, a mold having a microstructure forming a decorative element or photonic grid is used in one or another method of the invention. Thus, one of the arm 8, the rim 2 and the hub 4 has a structured surface quality. Only one part may have a structured surface quality or all parts of the balance may have a structured surface quality, which may be the same or different. Fig. 10 shows a balance of the invention, in which the felloe 2 has a structured surface quality different from that of the arm 8. Such structured surface quality may be in the form of polished, sanded, frosted, beaded, sunglowing, and the like. Microstructures forming a photonic network may also be provided in the mould used to make the balance, in order to replicate these microstructures on the surface of the balance. These microstructures may allow the creation of photonic crystals, giving the component a certain colour, hologram or diffraction pattern, which may constitute a security feature. These structures are introduced directly into the mould and are replicated by thermoforming during the production of the balance, which does not require any additional finishing operations. A logo may also be added to the mold.

The metal alloy used in the process of the invention typically has a coefficient of thermal expansion of less than 25 ppm/c and greater than 7 ppm/c and is capable of existing in an at least partially amorphous state when heated to a temperature between its glass transition temperature and its crystallization temperature.

The metal alloy used in the process of the invention is preferably based on an element selected from the group consisting of platinum, zirconium, titanium, palladium, nickel, aluminum and iron.

In the present description, the expression "based on an element" means that the above-mentioned metal alloy contains at least 50% by weight of the aforementioned element.

The above-described metal alloys for use in the present invention may be platinum-based and may have a coefficient of thermal expansion of less than 12 ppm/deg.C, preferably between 8 ppm/deg.C and 12 ppm/deg.C.

Such platinum-based metal alloys may consist of, in atomic percent:

platinum as the basic component, the amount of which constitutes the balance,

-13% to 17% of copper,

-3% to 7% of nickel,

-20 to 25% phosphorus.

The metal alloys used in the present invention may also be based on zirconium and may have a coefficient of thermal expansion of less than 12 ppm/c, preferably between 8 ppm/c and 11 ppm/c.

Such a zirconium-based metal alloy may consist of, in atomic percent:

zirconium as the basic component, the content of which constitutes the balance,

-from 14% to 20% of copper,

-12% to 13% of nickel,

-9% to 11% of aluminium,

-2% to 4% niobium.

The metal alloys used in the present invention may also be based on palladium and may have a coefficient of thermal expansion of less than 20 ppm/c, preferably between 13 ppm/c and 18 ppm/c.

Such palladium-containing metal alloys may consist of, in atomic percent:

palladium as the basic component, the content of which constitutes the balance,

-25% to 30% of copper,

-from 8% to 12% of nickel,

-18% to 22% phosphorus.

Ideally, the alloys used in the present invention do not contain any impurities. However, they may include trace impurities which are usually inevitably derived from the preparation of the above-mentioned alloys.

The alloys used in the present invention can be used to make at least part of a balance paired with a spiral spring, preferably made of monocrystalline quartz, if they have a coefficient of thermal expansion less than 12 ppm/deg.c and greater than 8 ppm/deg.c. The alloy used in the invention, which has a coefficient of thermal expansion of less than 20 ppm/deg.C and greater than 13 ppm/deg.C, can be used to make at least part of a balance to be paired with a spiral spring made of metal or silicon.

More preferably, the platinum-based metal alloy used in the present invention includes, in atomic percent: 57.5% Pt, 14.7% Cu, 5.3% Ni, and 22.5% P.

The coefficient of thermal expansion of this alloy is between 11 ppm/deg.C and 12 ppm/deg.C.

The above-mentioned zirconium-based metal alloy used in the present invention more preferably includes, in atomic percent: 58.5% Zr, 15.6% Cu, 12.8% Ni, 10.3% Al and 2.8% Nb.

The coefficient of thermal expansion of this alloy is between 10.5 ppm/deg.C and 11 ppm/deg.C.

The above-mentioned palladium-based metal alloy used in the present invention more preferably includes, in atomic percent: 43% Pd, 27% Cu, 10% Ni and 20% P.

The coefficient of thermal expansion of this alloy is between 15 ppm/deg.C and 16 ppm/deg.C.

The balance of the invention is therefore made of a material that makes it possible to use simple manufacturing methods, while having a coefficient of thermal expansion that allows them to be paired with spiral hairsprings made of monocrystalline quartz and/or metal or silicon, preferably made of monocrystalline quartz. The balance according to the invention can also have at least the arm with a coefficient of thermal expansion that allows it to mate with a spiral balance spring of monocrystalline quartz and/or metal or silicon, while having a high inertia by maintaining a compact and aesthetic rim geometry, with a small volume by means of a suitable rim either comprising a portion made of a higher density material or itself made of a higher density material.

Claims

1. Method for manufacturing a balance (1) for a timepiece, said balance (1) comprising a rim (2), a hub (4) and at least one arm (8) connecting said hub (4) to said rim (2), said hub (4) and said arm (8) being made of a metal alloy, said method comprising the steps of:

a) a mould made in the negative shape of the balance (1);

c) placing said metal alloy in said mould, heating said metal alloy to a temperature between its glass transition temperature and its crystallization temperature, so as to be thermally moulded and form a balance;

d) cooling said metal alloy to obtain a balance (1) made of said metal alloy;

e) releasing the balance (1) obtained in step d) from its mould;

the method comprises a step of overmoulding a first inertia adjusting member (10) in the rim (2), the first inertia adjusting member (10) being made of a first material having a density greater than the density of the metal alloy.

2. Method for manufacturing a balance for a timepiece, said balance comprising a rim (2), a hub (4) and at least one arm (8) connecting said hub (4) to said rim (2), said hub (4) and said arm (8) being made of a metal alloy, and said rim (2) being made of a second material having a density greater than the density of the metal alloy used for manufacturing said hub (4) and said arm (8), said method comprising the steps of:

a) a mold made in the negative shape of the balance;

a') inserting a rim or rim portions made of a material having a density higher than that of the metal alloy into the mould;

c) placing the metal alloy in the mould, heating the metal alloy to a temperature between its glass transition temperature and its crystallisation temperature so as to be hot moulded, and overmoulding the felloe or the felloe portion so as to mould a balance with an insert;

d) cooling the metal alloy to obtain a balance wheel with an insert;

e) releasing the balance obtained in step d) from its mould.

3. A method according to claim 1 or 2, wherein the rim (2) comprises a groove (12) designed to receive a second inertia adjustment and/or unbalance compensation member (14, 15).

4. Method according to claim 1 or 2, characterized in that the rim (2) comprises a groove (12) designed to receive a decorative and/or luminous element.

5. Method according to claim 1 or 2, characterized in that it comprises a step for overmoulding a flexible centring member (16, 17) in the hub (4).

6. Method according to claim 5, characterized in that the integrated flexible centering member (16) is located on the inner circumference of the hub (4).

7. A method according to claim 1 or 2, characterized in that it comprises a step of overmoulding a third flexible inertia adjustment member (19, 20, 22a, 22b) in the arm (8).

8. A method according to claim 1 or 2, wherein the mould has a microstructure forming a decorative piece or a photonic grid.

9. The method according to claim 1 or 2, characterized in that the metal alloy is based on an element selected from the group consisting of platinum, zirconium, titanium, palladium, nickel, aluminum and iron.

10. The method according to claim 1 or 2, wherein the metal alloy is based on platinum and has a coefficient of thermal expansion of less than 12ppm/° c.

11. The method of claim 10, wherein the metal alloy is platinum-based and has a coefficient of thermal expansion between 8ppm/° c and 12ppm/° c.

12. The method of claim 10, wherein the platinum-based metal alloy consists of, in atomic percent:

platinum as the basic component, the amount of which constitutes the balance,

-13% to 17% of copper,

-3% to 7% of nickel,

-20 to 25% phosphorus.

13. The method according to claim 1 or 2, wherein the metal alloy is based on zirconium and has a coefficient of thermal expansion of less than 12ppm/° c.

14. The method according to claim 13, wherein the metal alloy is based on zirconium and has a coefficient of thermal expansion between 8ppm/° c and 11ppm/° c.

15. The method of claim 13, wherein the zirconium-based metal alloy consists of, in atomic percent:

zirconium as the basic component, the content of which constitutes the balance,

-from 14% to 20% of copper,

-12% to 13% of nickel,

-9% to 11% of aluminium,

-2% to 4% niobium.

16. The method of claim 1 or 2, wherein the metal alloy is palladium based and has a coefficient of thermal expansion of less than 20ppm/° c.

17. The method of claim 16, wherein the metal alloy is palladium based and has a coefficient of thermal expansion between 13ppm/° c and 18ppm/° c.

18. The method of claim 16, wherein the palladium-based metal alloy consists of, in atomic percent:

palladium as the basic component, the content of which constitutes the balance,

-25% to 30% of copper,

-from 8% to 12% of nickel,

-18% to 22% phosphorus.